Rescue crews in Australia's fire-scorched areas are set to resume searching for victims Tuesday for a fourth day, as officials said they expect the current death toll of 173 to rise significantly.

As investigators struggled to determine how many of the hundreds of fires that tore across Victoria state since Saturday were deliberately set, hundreds of relatives and friends waited anxiously for news about the dozens still missing.

Family members comfort each other in Marysville, north of Melbourne, on Monday. ((Associated Press))

More than 4,000 firefighters from across the country are currently battling the fires, which are now threatening to expand into other areas around the state's capital, Melbourne.

Tuesday's weather calls for isolated showers in some areas, but others are expected to see a continuation of dry, hot conditions and possible ember attacks on rural areas northeast of the city.

Throughout Monday, firefighters found the charred bodies in cars of people who had tried to flee the fast-moving fires, while others were found in their homes.

Tony Bearzatto, the state duty officer with the Country Fire Association, said the bodies have been spread throughout a number of devastated areas.

"Unfortunately, the numbers are continuing to rise," he said.

More than 700 homes destroyed

Roughly 750 houses have been destroyed and 2,200 square kilometres of land charred by the fires, which continue to burn across Victoria and the neighbouring state of New South Wales. ((CBC))

Roughly 750 houses have been destroyed and 2,200 square kilometres of land charred by the fires, which continue to burn across Victoria and neighbouring New South Wales states.

Police have sealed off Marysville, a town destroyed by fire, telling residents who fled and news crews they could not enter because there were still bodies in the streets. Armed police moved through the shattered landscape taking notes, news photographs showed.

The town of Kinglake, north of Melbourne, was also razed by the fires. Resident Mark Strubing said he and a companion took refuge in a drainage pipe as his property outside the town burned.

"We jumped in the car and we were only literally just able to outrun this fire. It was travelling as fast as the wind," Strubing told Nine Network television news.

He said he and his friend rolled around in the water at the bottom of the pipe to wet their clothing as the flames swept past.

"How we didn't burn I don't know," he said.

One resident, Christopher Harvey, told Reuters the charred remains of the town looked like Hiroshima, the Japanese city hit by a nuclear bomb during the Second World War.

Harvey said people were dead in their houses and animal carcasses are all over the roads.

PM decries suspected arson as 'mass murder'

Australian Prime Minister Kevin Rudd, visibly upset during a television interview Monday, reflected national disgust at the idea the fires were started by arson.

"What do you say … about anyone like that? What do you say? " Rudd said. "There's no words to describe it, other than it's mass murder."

Christine Nixon, the chief police commissioner of Victoria state, said Monday some areas are being treated as crime scenes and that an arson task force will likely be established. She also warned the death toll will rise.

"We're expecting that we may find more people as we gain access to different parts of where the fires have been, and we think we may well find more who have died," Nixon said.

"What we've seen, I think, is that people didn't have enough time, in some cases. We're finding [bodies] on the side of roads, in cars that crashed."

Despite all signs indicating arson, the greatest problem for investigators is finding the evidence to prove it, freelance journalist Roger Maynard told CBC News on Monday in an interview from Sydney.

"Obviously, a lot of evidence will have been destroyed in the intensity of the fire," Maynard said.

Bearzatto said offers of help have come from around the world, including "the United States, New Zealand and other countries." He didn't specify if Canadian firefighters have offered their assistance.

Lawrence Cannon, Canada's minister of foreign affairs, expressed Canada’s sympathies to those affected by the bushfires.

"On behalf of the government and people of Canada, I wish to extend my deepest condolences to families who have lost loved ones," Cannon said in a statement on Monday.

"Our thoughts are also with the families who have lost their homes in the disaster and with those communities affected by these tragic events."

With files from the Australian Broadcasting Corp. and the Associated Press